A method and an apparatus of this kind are disclosed in document EP 1 321 562 A2. In said document a method and an apparatus are attuned to a problem in which a piece of cotton textile tends to shrink if dried at a relatively high temperature in a conventional washer-dryer. Accordingly, document EP 1 321 562 A2 specifies that the said drying procedure takes place at a temperature that is reduced in comparison with an initial temperature if the moisture in the drying piece of textile, as determined by a suitable sensor, drops below a specified point. The determining thermodynamic laws dictate that a temperature reduction in an air flow that contains water vapor implies a reduction in the partial water vapor pressure in the said air flow, though document EP 1 321 562 A2 contains no proposal or theory in this regard.
Instructions on the construction and operation of an apparatus for drying a piece of textile, as embodied in a conventional washer-dryer, emerge from document EP 1 321 562 A2 and from document EP 1 321 563 A2. The disclosures in the said documents are accordingly taken fully into account in the present disclosure.
An automatic washer-dryer is disclosed in U.S. Pat. No. 4,763,425. In the case of said washer-dryer, the temperature at which the washing is dried is controlled by reference to the type of textile of which the washed articles are made and the desired level of dryness required in said articles. The temperature is controlled by switching an electrical heating element on and off, holding the temperature constant to within a small margin, in particular plus or minus 5 degrees Fahrenheit (3 Kelvin), throughout the drying process.
An automatic washer-dryer is also known from U.S. Pat. No. 4,713,894. In such a washer-dryer, a drying piece of textile is impinged upon by an air flow to evacuate moisture, an oscillating partial pressure being generated in the air flow impinging on the piece of textile by switching a heating device on and off. For this purpose the washer-dryer disclosed in U.S. Pat. No. 4,713,894 varies the temperature of the air flow between 96.11° C. and 101.67° C. (a difference of 5.56 Kelvin).
A textile material that is built up in layers, one of which is known as a functional membrane, and is a semipermeable membrane allowing water vapor to pass through but keeping out water in liquid form, is widely used in sports outfits, rainwear and winter clothing, since material of said kind has particularly favorable wear characteristics. Such functional membranes are marketed under the brand names GoreTEX and Sympatex. Although in principle such material requires no specific precautions to be taken to protect the functional membrane during washing or cleaning, nevertheless a problem arises when drying a damp piece of this type of textile in a conventional washer-dryer: Since liquid water cannot penetrate a functional membrane of said kind, it is not possible to dry a piece of textile of this type uniformly in a conventional drying process. Since moisture shielded by the functional membrane from the air flow used for drying cannot access the air flow while in the form of moisture, it must be evaporated in order to make its way out through the functional membrane and reach the air flow. In the case of a piece of textile that includes a functional membrane, the conventional drying process performs in this way to only a limited extent and takes significantly longer.